Inulin and Oligofructose
Fructans are widely found in nature, being the most abundant nonstructural natural polysaccharides, present in a wide range of plants, some bacteria and fungi. Inulin represents a reserve carbohydrate enabling plants to survive during winter. Inulin and oligofructose have long been part of human diets. They may be combined easily with other ingredients without modifying delicate flavors of foods like milk. They have a low viscosity and are moderately soluble in water. Oligofructose is more soluble than inulin. In its pure form, it is about 35% less sweet than sucrose, has a good stability during food manufacturing (e.g., heat treatment), even if the fi-bonds between the fructose units can be hydrolyzed in high acidic conditions. Oligofructose shows humectant properties, reduces water activity to facilitate a high microbiological stability, and affects boiling and freezing points.
Inulin and oligofructose for their nutritional and their technological properties can offer a double benefit: an improved organoleptic quality and a better-balanced nutritional composition. Their solubility allows fiber incorporation in watery systems like drinks, dairy products, and table spreads. They are also used in functional foods, especially in dairy products and in bakery products such as breads, as prebiotic ingredients to stimulate the human microbiota system. For example, inulin enables, thanks to its gelling characteristics, the development of low-fat foods without compromising the taste or texture. Inulin may be a good ingredient to replace significant amounts of fat and improve the stability of the emulsion. Inulin may be also utilized in small amounts in low-fat dairy products, such as milks, fresh cheeses, yogurts, creams, desserts, to impart a better-balanced round flavor and a creamier mouthfeel. In frozen desserts, inulin can facilitate easy processing, a rich, creamy mouthfeel, and melting properties. Oligofructose is often used in replacement of sugar, for fiber enrichment, and better moisture retention. It has good binding characteristics for use in cereal bars. Oligofructose is a good solution as an ingredient to give bulk with less calories and to provide nutritional benefits without compromising the taste and mouthfeel.
From a nutritional point of view, inulin and oligofructose can improve the diet balance, thanks to their low energy value (1.5 kcal/g), however limited to the contribution of short chain fatty acids (SCFA) produced by fermentation and partially metabolized in the body. Inulin and oligofructose can be used by diabetics because they are not digestible, do not directly affect glycemia, nor glucagon or insulin secretion. The ingestion of inulin and or oligofructose has positive benefits on metabolic activity of beneficial bacteria of the colon—in particular, of bifidobacteria and some species of lactobacilli. The prebiotic intake significantly increased bifidobacteria and lactobacilli in both the proximal and distal parts of the colon (Roberfroid et al., 1998).
The microbial ecosystem plays an important role in maintaining good health. Imbalances in the composition of the gut microbiota have been linked to the several disorders. The prebiotic and bifidogenic effect of fructans has been demonstrated in vitro models, in animal studies, and also in human intervention studies (Roberfroid et al., 1998; Salzar et al., 2014). These studies have demonstrated a major shift in the intestinal bacterial composition, with bifidobacteria significantly increasing in numbers, whereas pathogens, such as clostridia, decreased in numbers.
The important bifidogenic properties of inulin and oligofructose, based on available data, seem independent of fructan chain lengh. In vitro experiments have shown that the length of the fructan chain is able to manage the rate of fermentation of the colon. The positive scientific evidences (in vivo studies) generated a “second generation” of prebiotics. The application of inulin and oligofructose has been studied in vitro and in animal models for the prevention and treatment of intestinal disorders (e.g., bowel inflammation, IBS, traveler's or antibiotic-associated diarrhea). Human studies (clinical trials data) demonstrated that inulin and oligofructose helped to reduce the balance of an altered gut microflora and can accelerate the recovery of the gastrointestinal tract (Frank and Alexiou, 2009). Inulin and oligofructose, in particular together, seem to improve the biomechanical properties of bones (femur resistance to fracture). Different studies were conducted in adolescent girls with adequate calcium intakes. The data have shown a significant increase in calcium absorption in comparison with placebo group. Positive effects of these two prebiotics were also observed in post-menopausal women, supplemented with 10g/day resulting in a significant increase in both calcium and magnesium absorption (Holloway et al., 2007).
The effects of inulin and oligofructose on appetite regulation and energy intake have been investigated in humans in a placebo-controlled, single-blinded intervention study involving ten healthy volunteers receiving oligofructose or a placebo (8 g twice daily). Oligofructose intake resulted in increased satiety, reduced hunger, and prospective food consumption. Another intervention trial in adolescents (total 100 subjects) demonstrated that the daily intake (8 g) of oligofructose and inulin (together) significantly reduced the body mass index (BMI), the body weight gain, and the body fat mass. Also, lipid metabolism may be improved by daily intake of inulin, as observed in different human studies—in particular, in slightly hyper-lipidemic subjects (Davidson et al, 1998; Letexier et al., 2003).